Cesium carbonate → 1-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-6-(methylsulfonyl)-1H-indol-2-yl)-2-methylpropan-1-one

Participants

Reaction Steps

To a stirred solution of 1-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-1,6-bis(methylsulfonyl)-1H-indol-2-yl)-2-methylpropan-1-one (780 mg, 1.27 mmol) in THF/methanol (15 mL/15 mL) was added Cs2CO3 (1.25 g, 3.83 mmol) in one portion. The mixture was allowed to stir at rt for 4 h and concentrated in vacuo to afford the crude product 1-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-6-(methylsulfonyl)-1H-indol-2-yl)-2-methylpropan-1-one. It was used for the next step reaction without further purification. To a solution of crude 1-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-6-(methylsulfonyl)-1H-indol-2-yl)-2-methylpropan-1-one, 2-(Boc-amino)ethyl bromide (2.8 g, 12 mmol) and tetrabutylammonium iodide (235 mg, 0.63 mmol) in CH2Cl2/toluene (2 mL/4 mL) was added 40% NaOH aq. solution (20 mL). The mixture was allowed to stir at rt for 20 h. The reaction mixture was diluted with CH2Cl2 (40 mL) and washed with H2O (50 mL). The organic layer was separated, and the aqueous layer was extracted with CH2Cl2 (4×50 mL). The combined organic solution was washed with brine, dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The residue was purified by flash chromatography over silica gel eluting with CH2Cl2/methanol (95/5) to provide tert-butyl (2-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-2-isobutyryl-6-(methylsulfonyl)-1H-indol-1-yl)ethyl)carbamate (300 mg, 35% yield for two steps). For 1-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-6-(methylsulfonyl)-1H-indol-2-yl)-2-methylpropan-1-one: LC-MS m/z 556 [M+Na]+. For tert-butyl (2-(5-(((tert-butyldiphenylsilyl)oxy)methyl)-2-isobutyryl-6-(methylsulfonyl)-1H-indol-1-yl)ethyl)carbamate: LC-MS m/z 699 [M+Na]+. 1H NMR (400 MHz, CDCl3): δ 8.20 (s, 1H), 7.93 (s, 1H), 7.72 (dd, J1=8.0 Hz, J2=1.6 Hz, 4H), 7.47-7.35 (m, 7H), 5.21 (s, 2H), 4.72 (d, J=6.8 Hz, 2H), 3.55 (d, J=6.8 Hz, 2H), 3.33-3.26 (m, 1H), 3.00 (s, 3H), 1.46 (s, 9H), 1.30 (d, J=6.4 Hz, 3H), 1.28 (d, J=6.4 Hz, 3H), 1.11 (s, 9H).

Provenance & Evidence